In prewind-type cameras, a prewound filmstrip roll contained in a film supply chamber of a lighttight camera body is advanced in a frame-by-frame manner into a film cartridge separately contained in an adjacent chamber of the camera body. After all of the exposures of the filmstrip roll have been taken, the film cartridge can be removed from the camera body for processing without requiring a separate film rewind, required in conventional wind cameras. Examples of prewind cameras include the so-called single-use cameras manufactured by Eastman Kodak Company and Fuji Photo Film Co., Ltd., such as those described in U.S. Pat. Nos. 4,884,087, 4,954,857, and 4,972,649 among others.
A problem confronted in the assembly of prewind cameras is that the unexposed filmstrip roll must be preloaded into an open side of the film roll chamber and then the camera body must be made lighttight, such as by the attachment of a rear cover which covers the open side of the film roll chamber. Simply releasing the film roll once loaded in the chamber, however, causes clockspringing, an expansion or detensioning of the film roll which must be prevented prior to the assembly of the rear lighttight cover to the camera body.
Numerous attempts have been made to solve the problem of clockspringing. In one such attempt, the mouth of the film roll chamber is made smaller than the cavity portion of the chamber. Other attempts require the use of additional supporting parts which must be added to force constraining of the film roll at least until the cover can be assembled to the rear of the film roll chamber.